diff --git a/css/css-typed-om/interfaces.html b/css/css-typed-om/interfaces.html
index e5a3638b8e6a65..d21f3f46984003 100644
--- a/css/css-typed-om/interfaces.html
+++ b/css/css-typed-om/interfaces.html
@@ -6,23 +6,73 @@
 <script src="/resources/testharnessreport.js"></script>
 <script src="/resources/WebIDLParser.js"></script>
 <script src="/resources/idlharness.js"></script>
+
+<style>
+  body {
+    font-size: normal;
+  }
+</style>
+
 <script>
 'use strict';
 
-promise_test(t => {
-  return fetch('/interfaces/css-typed-om.idl')
-    .then(response => response.text())
-    .then(idls => {
-      var idl_array = new IdlArray();
-      idl_array.add_idls(idls);
-      idl_array.add_untested_idls('interface Element {};');
-      idl_array.add_untested_idls('interface CSSStyleRule {};');
-      idl_array.add_untested_idls('interface ElementCSSInlineStyle {};');
-      idl_array.add_objects({
-        // TODO: Add more objects.
-      });
-      idl_array.test();
-      t.done();
+idl_test(
+  ['css-typed-om'],
+  ['cssom', 'SVG', 'geometry', 'html', 'dom'],
+  idl_array => {
+    try {
+      self.styleMap = document.styleSheets[0].rules[0].styleMap;
+    } catch (e) {}
+
+    try {
+      self.unitValue = CSSStyleValue.parse('height', '10px');
+    } catch (e) {}
+
+    try {
+      self.mathSum = CSSStyleValue.parse('width', 'calc(100% - 32px)');
+    } catch (e) {}
+
+    try {
+      self.transformValue = CSSStyleValue.parse('transform', 'translateX(0)');
+    } catch (e) {}
+
+    try {
+      self.rotate = CSSStyleValue.parse('transform', 'rotateX(0)')[0];
+    } catch (e) {}
+
+    try {
+      self.scale = CSSStyleValue.parse('transform', 'scale(1)')[0];
+    } catch (e) {}
+
+    try {
+      self.skew = CSSStyleValue.parse('transform', 'skew(0,0)')[0];
+      self.skewX = CSSStyleValue.parse('transform', 'skewX(0)')[0];
+      self.skewY = CSSStyleValue.parse('transform', 'skewY(0)')[0];
+    } catch (e) {}
+
+    try {
+      self.perspective = CSSStyleValue.parse('transform', 'perspective(0)')[0];
+    } catch (e) {}
+
+    try {
+      self.matrix = CSSStyleValue.parse('transform', 'matrix(0, 0, 0, 0, 0, 0)')[0];
+    } catch (e) {}
+
+    idl_array.add_objects({
+      StylePropertyMap: ['styleMap'],
+      CSSUnitValue: ['unitValue'],
+      CSSMathSum: ['mathSum'],
+      CSSTransformValue: ['transformValue'],
+      CSSTranslate: ['transformValue[0]'],
+      CSSRotate: ['rotate'],
+      CSSScale: ['scale'],
+      CSSSkew: ['skew'],
+      CSSSkewX: ['skewX'],
+      CSSSkewY: ['skewY'],
+      CSSPerspective: ['perspective'],
+      CSSMatrixComponent: ['matrix'],
     });
-}, 'CSS Typed OM IDL test');
+  },
+  'CSS Typed OM IDL test'
+);
 </script>
diff --git a/interfaces/css-typed-om.idl b/interfaces/css-typed-om.idl
index 45df5205d9a0a9..fa20d2d9bb800a 100644
--- a/interfaces/css-typed-om.idl
+++ b/interfaces/css-typed-om.idl
@@ -1,6 +1,7 @@
 // GENERATED CONTENT - DO NOT EDIT
-// Content of this file was automatically extracted from the CSS Typed OM spec.
-// See https://drafts.css-houdini.org/css-typed-om/
+// Content of this file was automatically extracted from the
+// "CSS Typed OM Level 1" spec.
+// See: https://drafts.css-houdini.org/css-typed-om-1/
 
 [Exposed=(Window, Worker, PaintWorklet, LayoutWorklet)]
 interface CSSStyleValue {
@@ -153,6 +154,14 @@ interface CSSMathMax : CSSMathValue {
     readonly attribute CSSNumericArray values;
 };
 
+[Exposed=(Window, Worker, PaintWorklet, LayoutWorklet),
+ Constructor(CSSNumberish min, CSSNumberish val, CSSNumberish max)]
+interface CSSMathClamp : CSSMathValue {
+    readonly attribute CSSNumericValue min;
+    readonly attribute CSSNumericValue val;
+    readonly attribute CSSNumericValue max;
+};
+
 [Exposed=(Window, Worker, PaintWorklet, LayoutWorklet)]
 interface CSSNumericArray {
     iterable<CSSNumericValue>;
@@ -167,11 +176,9 @@ enum CSSMathOperator {
     "invert",
     "min",
     "max",
+    "clamp",
 };
 
-// FIXME: Uncomment this when IDLHarness supports CSS namespaces:
-// https://github.com/web-platform-tests/wpt/issues/7583
-/*
 partial namespace CSS {
     CSSUnitValue number(double value);
     CSSUnitValue percent(double value);
@@ -220,7 +227,6 @@ partial namespace CSS {
     // <flex>
     CSSUnitValue fr(double value);
 };
-*/
 
 [Exposed=(Window, Worker, PaintWorklet, LayoutWorklet),
  Constructor(sequence<CSSTransformComponent> transforms)]